I'm loving what I've seen so far. I DMed a couple of sessions using the first playtest packet back in 2012, and we had a lot of fun with that. I get a strong vibe of B/X, BECM(I), and RC D&D out of these Basic Rules, but with more modern mechanics and design sensibilities.
I absolutely love how the backgrounds with their traits, bonds, and flaws are prominent in even the stripped-down version of the game. They aren't tacked on in some appendix, they are an integral part of the character creation system. Players who like coming up with their own backstories and character profiles can still do so, and players who don't want to do that can still have characters that have some grounding in the game world.
I've grown weary of class and race splatbooks, and I hope we don't see very many in 5e, but I would definitely buy a book that was full of new well-developed backgrounds and expanded traits, bonds, and flaws.
I really liked what 4e was doing with backgrounds, but they only appeared in PHB2 and the later splatbooks, and they were limited in what they could provide to the character as they weren't part of the original design.